1. Field of the Invention
The present invention relates to an image coding method, an image coding apparatus and an image pickup apparatus and it particularly relates to method and apparatus capable of coding images with different image qualities for each region as well as an image acquiring apparatus therefor.
2. Description of the Related Art
At ISO/ITU-T, JPEG2000 using a discrete wavelet transform (DWT) is being standardized as a successor to JPEG (Joint Photographic Expert Group), which is a standard technology for compression and coding of still images. In JPEG2000, a wide range of image quality, from low bit-rate coding to lossless compression, can be coded highly efficiently, and a scalability function, in which the image quality is gradually raised, can be realized easily. Furthermore, JPEG2000 comes with a variety of functions which the conventional JPEG standard did not have.
As one of the functions of JPEG2000, the ROI (Region-Of-Interest) coding is standardized, in which a region of interest of an image is coded and transferred in preference to other regions. Because of this ROI coding, when the coding rate has an upper limit, the reproduced image quality of a region of interest can be raised preferentially, and also when a codestream is decoded in sequence, a region of interest can be reproduced earlier with high quality.
Reference (1) listed in the following Related Art List discloses a technology in which a plurality of ROI regions within image data are automatically recognized.
Related Art List
    (1) Japanese Patent Application Laid-Open No. 2004-72655.
As described in the paragraph [0079] of the above Reference (1), when an image pickup apparatus is in the video shooting mode, the ROI is automatically set for the image of each frame shot. In the above Reference (1), however, there is a possibility that an undesired moving body, which is not intended by a photographer (user), might be set in the ROI region when a plurality of moving bodies are recognized in the image. Though it is described therein that user's favorite ROI regions can be selected from the plurality of ROI regions, it is troublesome to select such a ROI region per frame from the moving images and it is impossible to select the ROI regions during the shooting of moving pictures. Performing the recognition processing of ROI regions per frame results in a large amount of computation, thus increasing the signal processing load.